This invention relates to internal combustion engines and more particularly to methods and means for bypassing selected portions of unburned air-fuel mixture in the piston's crevice volumes to the engine crankcase for recycling to the induction system, thus reducing the exhaust of hydrocarbons from the engine combustion chambers on their respective exhaust strokes.
It has been hypothesized that unburned hydrocarbons in the exhaust gases of internal combustion engines include quench gases from the combustion chamber surfaces and crevice volumes in the spaces between the piston and cylinder wall where unburned mixture is present after the end of combustion in the engine cylinders. It is thought that such residual mixtures as are located near the vicinity of the exhaust valve are most likely to be swept out with the exhaust gases during the engine exhaust stroke. Unburned mixture forced into the piston-cylinder crevice volumes is expanded as cylinder pressures are reduced and thus passes out into the main body of the combustion chamber to be carried out with the exhaust gases.
Various means and methods have been proposed for preventing the exhaust of some of these unburned hydrocarbons and retaining or recycling them to the combustion chambers for burning. Two examples of prior art methods and arrangements are found in U.S. Pat. Nos. 3,667,443 Currie and Mick and 3,982,514 Turns and Siewert, both assigned to the assignee of the present invention. The arrangement of Currie and Mick vents the space between the piston and cylinder intermediate the first and second piston rings of an engine to bleed off unburned air-fuel mixture from this location below the top piston ring. Turns and Siewert disclose an arrangement for timed venting of portions of the combustion chamber walls to remove collected wall quenched combustibles therefrom and recycle them for reburning.